Rifled bore construction for a gun barrel



Aug. 25, 1970 Filed July 5, 1968 FAST BURNING RATE R. L. MARSHALL ET Al- RIFLED BORE CONSTRUCTION FOR A GUN lBARREL 2 Sheets-Sheet l LENGTH OF TRAVEL IN INCHES RICHARD L MARSHALL ANTHONY A BY 62m n ATT-05mg???` Aug. 25, 1970 R. L. MARSHALL ET Al- 3,525,172

RIFLED BORE CONSTRUCTION FOR A GUN BARREL 2 Sheets-Sheet :2

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United States Patent O U.S. Cl. 42-78 8 Claims ABSTRACT OF THE DISCLOSURE A gun barrel construction having a rified portion extending from the breech toward the muzzle end and terminating at the point where the pressure of released gases from the explosive charge of a cartridge used with the gun barrel is a maximum. The remaining portion of the gun barrel is smooth bored and acts as a frictionless guide for the projectile passing therethrough at increasing velocities.

This application is a continuation-in-part of application Serial No. 625,107, now abandoned, filed Mar. 22, 1967.

The invention relates to improvements in fire arms and more particularly to the ybarrel portion thereof.

Heretofore gun barrels have been usually provided with riiiing from breech to muzzle for the purpose of imparting a rotary motion twist to a projectile as it proceeds from the chamber or breech to the muzzle. Various attempts have been made to alter the inside diameter or bore of the barrels of firearms in an effort to increase the muzzle velocity of a projectile which is impelled by a given charge of powder or explosive.

In some instances in the prior art the bore of the barrel has been increased intermediate the breech and the muzzle, the bore adjacent the breech and muzzle lbeing of a reduced diameter. In others the rifling has been tapered toward the muzzle or completely eliminated adjacent the muzzle; however, the inside diameter of the barrel is usually reduced toward the muzzle which effects the choke to some degree and necessarily increases the friction and resistance between the projectile and the barrel.

Thus, although there have been various attempts by those skilled in this art to try to attain some means by which they could increase the speed or velocity of a bullet while it is still within the gun barrel, without sacrificing accuracy, no one has ever been successful, since they never recognized the principal reasons for the sudden or immediate decrease in speed or velocity of the bullet upon its being ejected from the terminus of the muzzle. Actually, it has been considered `by many that the maximum velocity of a bullet is at the end of the muzzle of the gun; however, as will be pointed out hereinafter, this has been found not to be true.

It also has been proposed, and experiments conducted in order to try to increase the speed of a bullet through the riding in the barrel of a gun, to increase the explosive grain content of a bullet to provide additional power to eject the bullet from the muzzle. However, by using this concept, speed of the projectile is not sufficiently increased to justify the detrimental effects on the barrel rifling, such as much more rapid erosion, the additional cost for a higher powered bullet, more frequent cleaning, greater recoil, etc.

Moreover, it had been thought necessary heretofore that it was essential for the proper design of a rifle to provide a barrel of sufiicient length to enable full acceleration of the bullet before ejection from the muzzle and to form the entire barrel perfectly with suitable riing 3,525,172 Patented Aug. 25, 1970 to direct the bullet accurately at the time that it is ejected from the barrel toward the target.

Further, the rate of acceleration required to be effected within the length of the conventional rilie barrel has introduced a considerable amount of recoil in the rifle, whereby the user is exposed to a rather large kick-back which makes it difiicult to control the barrel and its effective use is limited to persons capable of withstanding the resultant shock.

Normally, using an ordinary explosive technique for the bullet, the velocity of the rie `bullet from the very start is too low for maximum effectiveness, that is, i.e. about 2,500 ft. per second.

Furthermore, it has been learned that the maximum effective velocity of the bullet is not at the point where it is ejected from the muzzle of the gun barrel, but rather is at a relatively fixed point located at a critical distance measured from the breech of a gun barrel and that the inclusion of rifling in the gun barrel beyond this point, which will be later herein referred to as the peak pressure point attainable by any given quantity of explosive powder, only provides an additional friction drag on the bullet as it travels through the remainder of the rifling thus quite substantially reducing the maximum velocity of the bullet when it leaves the barrel.

The primary object of the invention, therefore, is to provide an improved gun barrel, the riding in the bore of which adjoins a cylindrical portion having a constant diameter throughout its length and which extends to the muzzle, the juncture between the rifling and smooth bored portion being predeterminable to attain peak pressure and maximum velocity from the bullet when the fire power of the explosive and caliber of the rifle is known.

Another object of the invention is to provide an improved gun which may be fired more rapidly without increase in the heat of the barrel portion thereof.

Still another object of the invention is to provide a gun construction that will require less frequent cleaning and prevent erosion of the bore thereof.

A still further object of the invention is to provide a rifle construction `which will have much less recoil or kick-back, thus enabling an individual of much smaller stature to be able to re the gun incorporating this teaching therein with considerably greater accuracy.

Yet another object of the invention is to provide a gun construction capable of maintaining at least 50,000 p.s.i. and as great as 60,000 p.s.i. on the projectile as it is ejected from the gun muzzle, thus maintaining greater velocity without loss of accuracy.

Still another object is to provide a gun barrel Ihaving sufficient riding extending from adjacent the breech end to impart adequate twist to the projectile to be discharged to insure accuracy in iiight and in which the land portions of the rifling are canted so as to offer less frictional surface to the projectile passing therethrough.

Other objects and advantages will become apparent from a reading of the following detailed description taken in conjunction with the drawings, in which:

FIG. 1 is a graph of diagram showing the relation between the velocity, discharge pressure, and barrel resistance during the passage of a projectile impelled by a fast burning powder through an ordinary gun barrel as compared to a gun barrel embodying the invention;

FIG. 2 is a longitudinal section of a gun barrel ernbodying the invention according to FIG. l;

FIG. 3 is a graph of diagram showing the relation between the velocity, discharge pressure, and barrel resistance during the passage of a projectile impelled by a slow burning powder through an ordinary gun barrel as compared to a gun barrel embodying the invention;

FIG. 4 is a longitudinal section of a gun barrel ernbodying the invention according to FIG. 3; and

FIG. 5 is an enlarged cross-sectional view of a portion of the ried bore shown in FIGS. 2 and 4.

The graphs shown in FIG. 1 and FIG. 3 designated as 23 and 23a are necessary by way of illustration and differ from each other according to the type of explosive and as will be explained more fully below.

Turning now to FIG. 2, there is shown in cross-section the barrel 12 of a gun constructed according to the principle of this invention with the breech portion thereof denoted as 13. Within the breech portion 13 of the barrel there is shown in elevation a cartridge 14 which includes a projectile 15. As also best shown in this view, the breech portion of the gun barrel is provided with riing 16 which terminates at the line 26-26 and adjoins a smooth bored area 18 having constant diameter throughout its length to the normal muzzle end of the gun barrel. There is also depicted at 17 in broken lines a projectile which, having been fired, is now traveling toward the muzzle.

In FIG. 1 of the graph the corner indicated as O and O is the point at which the explosive charge in a cartridge having a fast burning powder is activated and exerts pressure on a projectile. By a fast burning powder is meant those powders commonly known as:

Ball Nos.:

12758, Lake City Arsenal Military Powder 12338, Lake City Arsenal Military Powder 13-VH-l l, Winchester Western Powder 96-YC-03, Winchester Western Powder The amount of pressure exerted on a projectile from the time it is propelled from the breech end of a gun barrel until it leaves the muzzle end of the barrel of a rifle provided with a standard rifling throughout its length is indicated by the solid line 19 of FIG. l.

The inches of travel of a projectile from the breech to the muzzle of the barrel are indicated by the vertical lines 20 on the graph, and the pressure readings in pounds per square inch are read on the scale 21.

In the present illustration the pressure line 19 indicates that a maximum pressure of 50,000 pounds per square inch is reached at approximately 10.75 inches from the breech indicated by the vertical line 26-26 and decreases to approximately 30,000 pounds per square inch at the muzzle of a conventionally rifled barrel.

In FIG. l, the line 22 indicates the velocity of a projectile from the time it is propelled from the breech of an ordinary barrel until it leaves the muzzle end of the barrel at the rate of approximately 2,500 feet per second as read on the scale. At the distance indicated by the line 26-26 on the scale the velocity of the projectile is between 2,000 and 2,5 00 feet per second.

The line 24 of the graph in FIG. l indicates the bore resistance created by frictional drag on the lands of the riing by a projectile discharged in an ordinary rifle. The resistance in tons per square inch is read on the scale 25. The resistance in an ordinary barrel reaches a maximum of approximately 20 tons per square inch at line 26-26 or 10.75 inches from the breech of the barrel and decreases to slightly less than tons per square inch at the muzzle. The solid lines imposed on the graph indicate the performance of an ordinary rifle in which the diameter of the bore is uniform from breech to muzzle and the broken lines indicate the performance of a rifle embodying the invention illustrated in FIG. 2 using the same type of ammunition.

One of the purposes of this invention is to provide a gun barrel, the inside diameter of which is increased at a predetermined point and such enlargement continues uniformly from this point to the muzzle. Accordingly, the rie barrel shown in FIG. 2 has a uniformly enlarged portion 18 of constant diameter which is bored from the muzzle thereof to the point of peak pressure as indicated by the line 26-26.

At this time attention is directed to the upper portion of the scale of FIG. l and particularly the broken line 22. The line 26-26 on the scale corresponds to the line 26'-26 or the peak pressure point attained by the projectile when it is red from a gun barrel prepared as taught herein. The velocity from line 26-216 on the scale to the muzzle of the barrel increases from between 2,000 to 2,500 feet per second to between 3,500 and 4,000 feet per second as compared to a muzzle velocity of 2,500 per second with a conventional barrel.

In FIG. l the broken line 24' indicates the amount of bore resistance from the point 2\626 where the projectile enters the enlarged portion of the barrel 18. The resistance of a barrel embodying the invention drops from between l5 and 20 tons per square inch at the point of enlargement to approximately two and one-half tons per square inch as compared to a resistance approaching l5 tons per square inch with a conventional barrel. Thus, as depicted here it is apparent that frictional drag created by the thermal upset of the projectile after it is fired from the casing is a factor in substantially reducing the velocity of the projectile. The graph in FIG. l and the gun barrel shown in FIG. 2 are illustrative of a rifle barrel approximating that of a conventional .3080 rie or the M14 rie.

In opening up the barrel of a gun from the nozzle toward the rifling in the breech, it is necessary to predetermine beforehand the point where maximum or peak pressure of the explosive will be reached and experiments have shown that at this peak pressure point, this phenomenon also being denoted herein as maximum value, sufficient twist has been imparted to the projectile to provide accuracy in flight upon its being ejected from the muzzle. Although reference has been made to the fact that a conventional 7.62 mm. or the .3080 rifle has been the experimental weapon used herein, this teaching is applicable to any calibered rifle whether for sport or military use.

Turning now to FIGS. 3 and 4, it `will be seen that the graph shown in FIG. 3 is similar to that shown in FIG. l except that in this case the explosive charge in the cartridge is characterized by a slow-burning rate, such powder charges being commonly identified by Hercules Powder Corporation as: H.P.C. No. 12, lot No. 1; H.P.C. and H.C.F. No. 12/40 blend; H.C.F. No. 40, lot No. l; H.C.F. No. 30, lot No. l. Accordingly, the numerical designations in FIGS. 3 and 4 are the same as shown in FIGS. 1 and 2 except the suix a has been added. It will be seen from FIG. 3 that the line 26a-26a, which marks the peak pressure point on the line 19a as well as the high resistance point on the line 24a, is located at a distance of 11.50 inches from the breech 0f the barrel as shown by the line 26a-26cz in FIG. 3.

A rie constructed in accordance with this invention would have rifling suicient to impart a stabilizing twist to a projectile extending from the breech to a point in the barrel where the pressure behind the projectile would have reached the peak pressure. Thus, the velocity of the projectile is increased by decreasing the bore resistance at the point where the peak pressure has been attained and sucient twist is achieved through the riing adjacent the breech end of the barrel, this point being 10.75 inches from the breech for fast burning powders and 11.50 inches from the breech for slow burning powders.

Thus, in accordance with this teaching, a conventional rifle bore may be reamed from the muzzle end toward the point 26'-26, FIG. l, or 26d-26a', FIG. 3, and only sucient stock removed from the interior of the barrel to allow for thermal expansion of the projectile and permit free, smooth and unrestricted passage of the projectile from the point as defined above to the muzzle; the energy, which is normally wasted in overcoming the bore resistance of the rifling after peak pressure of the explosive and sufficient twist has been applied to the projectile for accurate flight has been attained, is then available to increase the velocity of the projectile.

It has been found that the barrel length of the gun does not atfect the velocity or accuracy of the projectile. For example, a -inch barrel will be as effective in imparting accuracy and speed to a projectile as a 26-inch barrel so long as the above requirements are met. Thus, it 'will be seen that the smooth bore portion of the barrel |12, 12a as shown in FIGS. 2 and 4 may vary in length as long as the ried portion 16, 16a is given a length in accordance with the principles of this invention.

The smooth bore portion 18 of the barrel 12, for example, is of a diameter such as to allow just enough gases to escape from the riiied portion 16 to act as a gas bearing surrounding the projectile traveling through the smooth bore portion. Thus, the projectile does not touch the surface of the bore which allows for maintaining a cooler barrel, as well as for thermal expansion of the projectile as it travels through the bore.

One of the important advantages derived from this invention is that a substantially smaller volume of powder charge than that ordinarily used in the magnums in current use can be used to impart the same velocities to the projectile as those achieved by the magnums used in conventional rifles. Por example, in an M-14 rie modiiied according to the principles of this invention, a 150 grain bullet, which is also used in the conventional M-14 rifle, can be packed with a powder charge of only 44.0 grains to achieve a velocity of 3,200 feet per second. In order to achieve this velocity with the magnums in normal use, it requires 86 grains of powder packed with the same 150 grain bullet. It will be seen, therefore, that the invention by its use of almost less than half the normal volume of powder will result in a substantial savings in cost.

As shown in FIG. 5, a further feature of this invention employs a canted construction of the land areas which make up the riiied portion 16 of the barrel 12. FIG. 5 shows in an exaggerated scale a portion of the canted land area 27 in which the rear edge deiines a distance a to the centerline of the bore which is larger than the distance b extending from the front edge of the land area 27 to the centerline of the bore. This construction allows for the projectile to slip through the riiied portion with less friction than that which is normally encountered with a conventional ritled construction since the projectile, which undergoes a twisting motion as it passes through the ried portion, is in effect only contacted by the leading edge of the land area constituting the ried portion of the bore. In practice, for a 22-caliber bore, the difference between a and b is .0009 inch. For a '3U-caliber bore, this dierence is .0010; for a 45-caliber bore the difference is .0015, and for a 50-ca1iber bore the diierence is .0016. Thus, it can be seen that with an increase in bore size, the degree of cant also increases. This relationship has proven to be the most eiective under actual test.

What is claimed is:

1. A gun barrel having a ried portion of a given inside diameter extending from a point adjacent the breech end thereof and terminating at a point 10.75 inches from the breech for fast burning powders where the pressure resulting from release of energy from an explosive charge of a cartridge used with said gun barrel is at a maximum (peak pressure), a smooth cylindrical portion of constant diameter extending from the muzzle end of said gun barrel and adjoining the terminus of said ried portion, and said smooth cylindrical portion having an inside diameter not less than the diameter ofthe consecutively grooved area confined between the lands of the ritling in said ried portion.

2. A gun barrel having a rifled portion of a given inside diameter extending from a point adjacent the breech end thereof and terminating at a point 11.50 inches from the breech for slow burning powders where the pressure resulting from release of energy from an explosive charge of a cartridge used with said gun barrel is at a maximum (peak pressure), a smooth cylindrical portion of constant diameter extending from the muzzle end of said gun barrel and adjoining the terminus of said ried portion, and said smooth cylindrical portion having an inside diameter not less than the diameter of the consecutively grooved area confined between the lands of the rifling in said rifled portion.

3. A gun barrel having a ried portion of a given inside diameter extending from a point adjacent the breech end thereof and terminating at a point 10.75 inches from the breech for fast burning powders where the pressure resulting from release of energy from an explosive charge of a cartridge used with said gun barrel is at a maximum (peak pressure), a smooth cylindrical portion of constant diameter extending from the muzzle end of said gun barrel and adjoining the terminus of said rifled portion, said smooth cylindrical portion having an inside diameter not less than the diameter of the consecutively grooved area confined between the land areas of the riing in said riiled portion, and the land areas of said ried portion are canted in the direction toward the muzzle end of said gun barrel and the rear edge of said land area defines a distance a to the center line of the bore which is larger than the distance b extending from the front edge of the land area to the centerline of the bore.

4. A gun barrel according to claim 3 wherein the degree of said cant varies for different size diameters of bore of said gun barrel.

5. A gun barrel according to claim 3 wherein the degree of cant of said land areas is larger for a given diameter of bore of said gun barrel than for a lesser diameter of bore of said gun barrel.

6. A gun barrel having a rifled portion of a given inside diameter extending from a point adjacent the breech end thereof and terminating at a point 11.50 inches from the breech for slow burning powders where the pressure resulting from release of energy from an explosive charge of a cartridge used with said gun barrel is at a maximum (peak pressure), a smooth cylindrical portion of constant diameter extending from the muzzle end of said gun barrel and adjoining the terminus of said rifled portion, said smooth cylindrical portion having an inside diameter not less than the diameter of the consecutively grooved area confined between the land areas of the riiling in said ried portion, and the land areas of said ried portion are canted in the direction toward the muzzle end of said gun barrel and the rear edge of said land area deines a distance a to the center line of the bore which is larger than the distance b extending from the front edge of the land area to the center line of the bore.

7. A gun barrel according to claim 6, wherein the degree of said cant varies lfor diterent size diameters of bore of said gun barrel.

8. A gun barrel according to claim 6, wherein the degree of cant of said land areas is larger for a given diameter of bore of said gun barrel than for a lesser diameter of bore of said gun barrel.

References Cited UNITED STATES PATENTS 460,102 9/ 1891 Carver 42-78 y804,483 11/ 1905 Lincoln 42-7 8 1,355,421 10/1920 Pedersen 42--78 1,355,422 10/ 1920 Pedersen 42-78 2,849,923 9/ 1958 Cotterman 42-78 2,990,342 6/ 1961 Sullivan 42-7 8 BENJAMIN A. BORCHELT, Primary Examiner C. T. JORDAN, Assistant Examiner U.S. Cl. X.R. 29-1.1; 42-76 

